1. Field of the Invention
This invention relates to a channel structure for flow of molten pig iron during tapping of a blast furnace, and also to a method of cooling such a structure. The channel structures employed for guiding the flow of molten pig iron from a blast furnace include firstly a main channel known as an "iron trough" which extends from the taphole and carries both iron and slag and secondly channels branching from said main channel known as "iron runners" and usually carrying either slag or iron.
2. Description of the Prior Art
Typically, such a channel structure comprises at least a wear lining which during operation provides a surface contacting the iron, a permanent lining in which the wear lining is contained, and a steel or concrete support outside the wear lining. A typical iron trough is for example ten to twenty meters long and three meters wide. Examples are shown in EP-A-90761 and EP-A-143971 where coolant passages are located in the lining layers, inwardly of the outer support, and EP-A-60239 where the metal support which is of channel shape has spaces in it for coolant, particularly air.
"Iron and Steel Engineer", October 1988, pages 47-51, especially FIG. 2 on page 48, describes a water-cooled iron trough having a wear lining, an alumina permanent lining, two carbon layers of high thermal conductivity outside the permanent lining and a steel box of channel shape which is water-cooled on all three sides.
It is noted here that the present invention is not limited to water-cooled channel structures, but also relates to air-cooled structures, and to structures which are cooled in other ways, for example with a glycol/water mixture, as is also described in the same article in the "Iron and Steel Engineer".
The wear lining of an iron trough or runner may for example consist of a refractory concrete. Carbon in Combination with aluminium oxide bricks may be used for the permanent lining, or for example just aluminium oxide bricks. The outer lining between the steel outer boundary of the permanent lining is for example made of graphite, carbon or semi-graphite.
On account of strength considerations, the steel of the outer support should achieve no temperature higher than about 200.degree. C. The pig iron comes out of the blast furnace directly into contact with the wear lining and has a temperature of about 1450.degree. C.-1550.degree. C. As a result substantial thermal stresses occur in the structure. The way in which this thermal load is accommodated in the design of the iron trough or runner largely determines the life of the iron runner.
A problem can for example be that, as a consequence of the thermal stresses, the iron trough or runner begins to crack, as described in copending application U.S. Pat. No. 447053 filed 5th January 1990 and not yet published and also copending European application 89203088, Australian application 46940/89 and Indian application 917/MAS/89, not yet published. This cracking leads to the defect that escaping liquid pig iron fills a space on the outside of the steel support, which makes repair expensive. To carry out the repair the iron trough or runner has to be removed completely at the position of the breakout in order to be able to remove the now solidified pig iron. After that the trough or runner has to be fitted again. All this is expensive. It also occurs that, because the trough or runner overflows, liquid pig iron falls into a space between the steel support and the "shore" which supports the iron trough or runner. Then too the solidified pig iron has to be removed and this has the same drawbacks as mentioned above.